Reduction of Solar Radiation by Manmade Aerosol and thus Modified clouds in Europe

Détails concernant le projet

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CSC - Cost-sharing contracts

Objectif

To assess the reduction of the solar flux by anthropogenicaerosol in Europe.

Aerosol particles in the atmosphere reflect solar radiation and thus form a cooling factor. The cooling induced by anthropogenic aerosol counterbalances the warming by the man made greenhouse gases. However, the magnitude of the compensation factor is very uncertain. The dominant problem in quantifying the 'aerosol' effect on radiation is the localized character of the aerosol.

The effect of anthropogenic aerosol on local radiation/climate in Europe is being assessed. This is realized along 3 interconnected approaches. In recent estimates of the reduction in radiation in Europe the value for light scattering by aerosol was taken from United States measurements. This value is compared with the actual value in Europe. Furthermore, the historical trend in solar flux is related to the historic trend in aerosol loadings. Finally, the full effect of aerosol on radiation/climate is modelled. The radiation module being developed is validated with special field campaigns. In these experiments the relevant aerosol characteristics are determined and from these the reduction in solar radiation is calculated and compared with the measured reduction.Aerosol particles reflect solar radiation back into space and thus lessheat reaches the earth surface. Aerosol does not intercept the outgoingterrestrial radiation and thus the net result is a cooling, which isestimated to compensate the warming by the greenhouse gasesin Europe.

Because of the very localized character of aerosol, a localizedassessment of the aerosol-forcing is required. This is realized alongthree interconnected approaches.

The recent estimates of the reduction in radiation by aerosol in Europeare extrapolations of ground-level light-scattering measurements in theUS. It is checked here which data are available in Europe and what theactual scattering by European aerosol is. The European aerosol has alarge nitrate-content and the light-scattering of this compound will bestudied in detail. These results will be used in support of the next twoapproaches.

A decrease in solar flux over the last decades has been observed in threecountries in Europe. Here, the trend on the cloudless days is analyzed.A search is made for available data on aerosol loadings in the sameperiod to be compared with the trend in the solar flux. The relation willgive an empirical factor for the aerosol forcing.

A simple 1-D version of the climate model ECHAM is made and aerosol isparametrized in this model, for a calculation of the local cooling effectof aerosol. First, the radiative forcing is calculated with a modulewhich uses the averaged parameters of the standardized "Climatology"aerosol. This aerosol seems outdated and new detailed measurements aremade to check its validity. Simultaneously, solar radiation and relevantmeteorological parameters are measured.The reduction in solar flux is calculated from the measured aerosolparameters and this is compared to the measured reduction in solar flux.The reduction will also be compared to the reduction calculated with the"Climatology" aerosol and so the best up-to-date aerosol parameters areobtained.A last validation of the aerosol/radiation model comes from a comparisonof modeled and measured trends in radiation.

A start is made of assessing which type of (anthropogenic) aerosolparticles serve as cloud nuclei for the climate-relevant clouds inEurope.